ARROW-11586: [Rust][Datafusion] Remove force unwrap

Fix for https://issues.apache.org/jira/browse/ARROW-11586

Closes #9479 from marcprux/patch-3

Authored-by: Marc Prud'hommeaux <marc@glimpse.io>
Signed-off-by: Andrew Lamb <andrew@nerdnetworks.org>
diff --git a/rust/datafusion/src/sql/planner.rs b/rust/datafusion/src/sql/planner.rs
index d2cbd7c..8d6ed7f 100644
--- a/rust/datafusion/src/sql/planner.rs
+++ b/rust/datafusion/src/sql/planner.rs
@@ -558,7 +558,7 @@
             .iter()
             .map(|e| {
                 Ok(Expr::Sort {
-                    expr: Box::new(self.sql_to_rex(&e.expr, &input_schema).unwrap()),
+                    expr: Box::new(self.sql_to_rex(&e.expr, &input_schema)?),
                     // by default asc
                     asc: e.asc.unwrap_or(true),
                     // by default nulls first to be consistent with spark